1. Field of the Invention
The present invention generally relates to an optical scanning device, and more specifically to an optical scanning device that supports a mirror supporting part from both sides in an axis direction by a pair of torsion beams, and drives the mirror supporting part so as to swing around the axis by twisting the torsion beams.
2. Description of the Related Art
Conventionally, an optical scanning device is known that includes a movable plate that reflects an incident light, a torsion beam that supports the movable plate in a rotatable way around an axial direction, and a drive part that gives a drive force in a twisting direction to the torsion beam, wherein a rib is formed at least in the vicinity of a connection between the movable plate and the torsion beam, as disclosed in Japanese Patent Application Laid-Open Publication No. 2010-128116 (which is hereinafter called “Patent Document 1”).
The optical scanning device disclosed in Patent Document 1 aims at suppressing a dynamic distortion of a reflecting plane without increasing a weight of the movable plate.
In recent years, optical scanning devices tend to be required to have higher resolution. To implement the higher resolution, a resonant frequency is needed to be raised, for which a rigidity of a torsion beam (which may be called a “torsion bar”) is needed to be increased.
Here, if a width of the torsion beam is broadened to improve the rigidity, since a deformed state of the torsion beam differs depending on a distance from a center axis of the torsion, a problem of nonlinearity of a displacement is caused.
In Patent Document 1, since such a problem of the nonlinear oscillation is not considered at all, if the resonant frequency is raised, the problem of the nonlinearity of the displacement is caused. Moreover, in the configuration described in Patent Document 1, an effect of preventing a mirror deformation is obtained, but a stress caused by the oscillation is not blocked, so if the resonant frequency is raised, the mirror deformation is not prevented.